docs: def _compute_distance_scaling(self, rup, dists, C):
          """
          Compute distance-scaling term, equations (3) and (4), pag 107.
          """
          Mref = 4.5
          Rref = 1.0
          R = np.sqrt(dists.rjb ** 2 + C['h'] ** 2)
          return (C['c1'] + C['c2'] * (rup.mag - Mref)) * np.log(R / Rref) + \
              C['c3'] * (R - Rref)